Review on Diamond Coated Cylinder Mounted Grinding by Raymundo Miller

Good bits for the price and quantity. They hold up quite well. I'm sure it depends on the material you're using it on. I use mine for stone with sharp edges and uneven, rough surfaces. And I use them A LOT. So I'll probably put the Beats through the ultimate test. And these have held up well. My only complaint is that some bits (about half of the ones I've bought) have worn down to metal on only one strip of the bit or just a piece of it (all the diamond coating was coming off). Which rendered it useless for my purposes after two or three uses. Again, this may be the material I use them on. Otherwise they are great. Now I'm ordering the next batch.